Both iPhone and BlackBerry will do what you want. It will be a matter of what your management is willing to spend on the required infrastructure to implement. The other cost to factor in is the tariff from the mobile providers. iPhone tariffs tend to be less expensive and more flexible, whereas BlackBerry devices require special data plans.

In Turkey, obviously Avea will be your cheap option, but you'll get better coverage from Turkcell and Vodafone in my experience. For business use, you should look to get a 2-4 GB data allowance on the tariff, which will run around 150-250TL monthly depending on whether your management is willing to sign a contract.